We have postulated that the site of action of anesthetics is not limited to the lipid part of the cell membranes and that the site may be at the water/macromolecule interface irrespective of lipids and proteins. Interaction of inhalation anesthetics with macromolecular structure is being investigated with synthetic polypeptides, natural proteins and surfactant micelles. In the present project, surfactant micelles are used as a simple macromolecular model because micelles contain well-defined hydrophobic core covered by the hydrophilic surface. By the use of anionic, cationic and non-ionic surfactants, it is possible to manipulate the surface charge characteristics of the micelles. These micelles undergo phase changes. These changes occur at points known as the critical micelle concentration, the Krafft point and the cloud point, which can be measured with great accuracy by the optical absorbance and electrical conductivity methods. The effects of inhalation anesthetics on the physical properties of the micelles represented by the above measurements will be analyzed by thermodynamics. The partition coefficients of the anesthetics between the micelles and aqueous phase and therefore, the standard free energy of the transfer of anesthetics will be obtained from the analyses. Since the partial derivative of the equilibrium quantity by pressure will reveal the volume change of the system, the pressure studies will be included. The thermodynamically obtained values for the volume change will be compared with those obtained by the direct measurement of the partial molal volume by high precision densimetry.